Sudden slow upstream rate on BT

I've been on BT Total Broadband for several years now. I'm about 5 Km from the Exchange so my downstream sync speed varies between 3500 and 4000 kbps. Upstream sync speed has been 448 for as long as I can remember. Lately I've been getting sudden resyncs where the downstream remains more or less the same but the upstream drops to 96 kbps. Can stay like that for a while until I force a reboot of the router. Happens with both Netgear DG834 and BT Home Hub 2.0 . BT Engineer has been to the house, checked the line and there are no faults (at least not at the time). Here are a couple of stats from the home hub at both times. SNR up is 21-23 db when it's 448 kbps but only 6 db when it's 96. The router is connected directly to the NTE5 master socket and there's no extension wiring. Any ideas anyone?

Downstream 3,712 Kbps
Upstream 448 Kbps
Noise margin (Down/Up) 12.9 dB / 21.0 dB
Line attenuation (Down/Up) 48.0 dB / 27.0 dB
Output power (Down/Up) 19.3 dBm / 11.9 dBm

***

Downstream 3,360 Kbps
Upstream 96 Kbps
Noise margin (Down/Up) 14.3 dB / 6.0 dB
Line attenuation (Down/Up) 49.0 dB / 28.0 dB
Output power (Down/Up) 18.9 dBm / 10.2 dBm

The upstream on standard ADSL uses frequencies 25.875 kHz to 138 kHz. The obvious answer is that you are getting general static within that range. Try to find the source (new business started up on your phone line route?).

p.s. Have any neighbours complained?

Edited by deleted (Fri 22-May-09 09:18:59)

Lately I've been getting sudden resyncs where the downstream remains more or less the same but the upstream drops to 96 kbps.

As the man said, it could be external interference in those lower frequencies.

Other possibilities include a filter failing and allowing interference from a phone - try it with only the router and no telephones connected.

Your router or the line card in the exchange could be on the way out, so borrowing an alternative router (BT ones are cheap on ebay) would rule one of those out.

Tried both Netgear DG834 and BT Home Hub 2.0 - both sync either correctly (at 448) or slowly at 96. This morning down to 64. Tried 3 different filters, disconnecting phone etc. to no avail. Yesterday evening at 21.00 it was stuck on 96 no matter what I did. Then BT India called for a status check and 20 seconds into the call the line re-synced itself back to 448 during the call itself. (Earlier in the day it was at 448 and a phone call from a neighbour caused a resync back to 96). BT are now going to start doing some diagnostics as the local engineer could find no problem with the line. This morning stuck on 96 again (then 64) after it dropped at 01.00. Got a phone call at 11am after which I tried another resync and it went straight back to 448. It looks to me like some sort of problem at the Exchange so I'll see what the BT diagnostics say. I've also had several problems recently where the ADSL link had dropped and the only way of getting it back was to make a phone call.

Glad to see you back posting. I did rather wonder what had happened to you.

Well I've had 2.5 years of very stable ADSL from BT until now so I'd sort of stopped worrying! Now I have a problem again. Seems upstream keeps switching between 96 kbps and 448. Whenever I find it on 96 I just call 0800 800150 and within 20 or so seconds the line re-syncs to 448. Sure there's an exchange fault somewhere so I'll keep on at BT. Incoming calls can sometimes also cause a re-sync.

The issue here is that downstream does not appear to be affected, so unless you go looking at your line stats you may not know you have a problem. Wonder how many other people are blissfully unaware?

Filters, or a fault that will eventually show up as audible during phone calls, you'll have to keep trying support

sounds like the beginning of a line fault - high resistance near-disconnect which is improved by the extra current flow during a call ?

Unfortunately the SLA is for 64k upstream minimum so you may have to wait for it to fail properly.

BT ran diagnostic tests last weekend and said "no network fault found". Since then for the last 6 days the line has been totally stable: downstream 3680 kbps and 448 up. This is more or less what I can expect given the distance from the exchange (about 4.5 Km). I assume whatever the problem was eventually became apparent and has been fixed though I don't know what it was.

Anyway thanks for your replies.

Well I spoke to soon - it's all gone pear-shaped again. BT Engineer has been to the house again and no fault found. He replaced the cable to the pole outside and the socket with a filtered ADSL one, but the line dropped overnight again. Now I'm waiting for an ADSL specialist to call.

What I can see from the BT Home Hub 2.0 stats is that the output power is normally 19.0 dbm downstream and 11.5 dbm upstream. When the line re-syncs at slow speeds the downstream is usually 19.0 but the upstream has always dropped to 9.5 dbm. I believe this means the power has dropped from 14.1mw to 8.9mw - almost a 40% reduction. Sometimes the downstream drops from 19.0 to 17.5, and when it does my sync speed is reduced from 3776 (typically) to 2326. Downstream line attenuation is 48 db and I can see the Target SNR is 12 db. Normal sync rates are 3776/448.

Am I right in assuming the power levels are set by the DSLAM in the exchange? I've tried both Home Hub and DG834 with the same problem on both. But if I make a simple phone call for 10-20 seconds (eg to BT help desk) and then disconnect/reconnect the phone line to the router, it resyncs correctly.